Nebulizer apparatus

ABSTRACT

A nebulizer apparatus to atomize liquid solutions or suspensions. The nebulizer is typically used in conjunction with a breathing circuit to deliver atomized medicine to a patient. A housing with an opening covered by a thin mesh plate is supplied with the liquid to be nebulized on an “on-demand” basis. The mesh plate or liquid is vibrated at ultrasonic frequencies to atomize the liquid as it passes through the plate into breathing gases flowing through the breathing tube.

BACKGROUND OF THE INVENTION

The present invention relates to an improved nebulizer apparatus.Nebulizers, or atomizers, are devices, which generate a fine spray oraerosol, usually of liquid. A particularly useful application fornebulizers is to provide a fine spray containing a dissolved or asuspended particulate or colloidal pharmaceutical agent foradministration to a subject by inhalation. Such inhalation treatment ishighly effective for conditions affecting the subject's respiratoryorgans. Further, since the lungs are close to the heart and the bloodcirculatory system of the body, drug administration by inhalationprovides an effective and rapid delivery system to all organs of thebody.

In many cases, the nebulizer is placed directly in the mouth or nose ofthe subject so that the spray can be entrained in the respiratory gasesinhaled during normal, spontaneous breathing of the subject. In othercases, the subject breathes with the aid of a respiratory ventilator. Atypical ventilator has a breathing circuit comprising an inhalation limband an exhalation limb connected to two arms of a Y-connector. The thirdarm of the Y-connector is connected, via a patient limb, to amouthpiece, mask or endotracheal tube for the subject. The ventilatorprovides a complete or partial supply of respiratory gases to thesubject through the inhalation limb during inhalation. The contractionof the subject's lungs discharges gas through the exhalation limb duringexhalation. When a nebulizer is employed in conjunction with aventilator, it is typically placed in the patient limb.

Nebulizers currently in use for ventilator applications generate thespray either pneumatically or by means of ultrasonic vibrations.Pneumatic nebulizers are typically used with a liquid, such as anaqueous drug solution. High pressure driving gas is conducted through anozzle to draw the drug from a drug supply for the nebulizer. The drugis discharged against a baffle or other means in a gas space of thenebulizer, breaking the liquid into a fine spray. The gas space is influid communication with the inhaled gas pathway of the breathingcircuit so that the gas flow expelled from the nozzle along with thenebulized drug is conducted to the breathing circuit and ultimately tothe subject.

Disadvantages in the use of pneumatic nebulizers include the following.If the nebulizer adds a significant quantity of gas, for example, up tofive liters/minute, into the breathing circuit, the breathing gascomposition is affected. The driving gas is most often either oxygen orair and, particularly when a ventilator is used in the treatment of achild, the gas flow from the nebulizer may form a major portion of theinhalation gas flow. Because of the gas flow from the nebulizer, controlover the inhalation gas composition is lost. Also, due to passage of thedriving gas through the nozzle, impingement of the drug on the baffle,etc., pneumatic nebulizers are noisy. This may contribute to thediscomfort of the subject. And, as controlling the commencing andstopping of a drug agent spray is difficult and is not very accurate,pneumatic nebulizers are commonly active during both inhalation andexhalation. This obviously decreases the efficiency of drug delivery asmeasured by ratio of the amount of drug supplied to the nebulizer andthe amount of drug actually delivered into the subject's air ways.

In an ultrasonic nebulizer, the fine spray is produced by ultrasonicvibration of the liquid, as by a piezoelectric crystal. The liquid isdropped on, or otherwise applied to, the crystal. The on-off operationof such nebulizers is easier to control than for a pneumatic nebulizer.However, prior art ultrasonic devices require a large electrical powerconsumption to power the crystal and may not be able to nebulizecolloidal or particulate suspensions. Partly due to the high powerconsumption of ultrasonic nebulizers, the equipment tends to be bulky.This can cause considerable difficulties, given the crowded environmentthat may surround a subject, such as a critical care patient.

U.S. Pat. No. 5,443,059, shows an attempt to solve the problem ofbulkiness in an ultrasonic nebulizer. In the '059 patent, a liquidsource and metering component are provided in separate control unit thatcan be located at a distance from the subject. The control unit metersliquid through a feed line to a piezoelectric ceramic plate positionedin the patient limb of the breathing circuit. The piezoelectric ceramicplate nebulizes the liquid. In the event more liquid is delivered thancan be nebulized, the device is equipped with a collection vessel forthe excess liquid. In the structure disclosed in this patent, themetering line for the liquid to be nebulized is located above thevibrating crystal so that the liquid drops onto the crystal. However,this renders the ultrasonic nebulizer of this patent position sensitive.Additionally, during inhalation, the flow speed of the respiratory gasescan exceed 10 m/s. Such a flow speed can draw the droplets of liquidaway into the respiratory gases without the droplets being applied tothe vibrating crystal for nebulization. This may render the inhalationtherapy less effective, or may alter dosage rates, both of which canadversely affect the subject.

U.S. Pat. No. 3,812,854 describes a nebulizer for inhalation therapy inwhich the spray is generated on the front surface of a vibrating, porousbody. The pores of the body form a network of passages that enable theliquid to flow through the body. The liquid to be nebulized is suppliedunder pressure from a liquid supply through a liquid conduit to thepores, and forced through the pores to the front surface of the porousbody where it is discharged as a spray.

However, the complicated flow paths in the porous body increase the flowresistance so that high liquid pressure is required to transport theliquid through the body. To resist the forces resulting from the highliquid pressure, a thick porous body is required. But, such thicknessincreases the weight of the nebulizer as well as the amount of electricpower required to vibrate same. Also, when used with suspensionscontaining suspended particulate or colloidal particles, the particlesmay be entrapped in the complicated flow paths through the porous body.

U.S. Pat. No. 5,478,378 describes a nebulizer in which the aerosol isformed using a mesh plate instead of a porous solid body, thereby tolessen or eliminate the foregoing shortcomings. The mesh plate has aplurality of orifices for the liquid in a reservoir. The orifices aretapered outwardly toward the outlet for the liquid. The liquid or thenozzle assembly is vibrated ultrasonically by a piezoelectric element tonebulize the liquid. The liquid reservoir is preferably permanentlyfilled with liquid and maintained at a slight negative pressure.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved nebulizerapparatus of the mesh plate type that can atomize both solutions andsuspensions without clogging. Another object of the invention is toprovide such an apparatus that has a liquid supply control means and ameans for substantially equalizing pressures in the nebulizer apparatuswith pressures in the breathing circuit. These means avoid pressurestressing of the mesh plate and avoid leaking of the liquid to benebulized through the mesh plate. Yet another object of the invention isto provide such an apparatus that has a relative small size and lowpower consumption thereby facilitating its use. Yet another furtherobject of the invention is to provide such an apparatus that isinsensitive to the position in which it is operated. An additionalobject of the invention is provide such an apparatus that has fastresponse to activation and deactivation, enabling nebulization to betriggered in response to the subject's breathing pattern. A furtherobject of the invention is to provide such an apparatus that efficientlytransforms all the liquid into an aerosol.

Provided in accordance with one aspect of the present invention is anebulizer apparatus for atomizing a liquid into fine droplets. Theaerosol so produced may contain medication to be delivered to breathinggases for a patient. In such an environment, the nebulizer apparatus ismounted in a breathing circuit adapter through which the breathing gasespass. The nebulizer has a housing. A mesh plate spanning a cavity in thehousing has one side exposed to the gases passing through the housing.The liquid to be nebulized flows into the cavity from a liquid transportline to a rear surface of the mesh plate. A vibration means vibrates theplate or liquid to cause the liquid to pass through holes in the meshplate to be broken up into droplets and discharged as an aerosol fromthe front surface of the mesh plate in the flow of breathing gases. Thevibrator means for vibrating the mesh plate or liquid is preferably apiezoelectric element energized by an ultrasonic frequency powerservice.

The mesh plate employed in the present invention is thin as compared tothe ceramic bodies used in prior art nebulizers. This permits reducedoperating pressures and forces, less energy to vibrate the plate, andallows the use of suspensions since particulates in a suspension canflow through the paths defined by the holes instead of the myriad ofcomplicated flow paths found in ceramic bodies.

The pressure at the rear surface of the mesh plate and at the frontsurface of the mesh plate is equalized to avoid stresses in the thinmesh plate. This equalization of pressure is accomplished by the use ofa pressure channel in the housing communicating between the cavity inthe housing and the breathing gas passage.

The delivery of liquid to be nebulized is preferably controlledresponsive to the amount of liquid at the rear surface of the meshplate. For this purpose, a sensor, such as a pair of electrodes spacedfrom the rear surface of the mesh plate, may be used for sensing thepresence of liquid at the rear surface of the mesh plate by changes inimpedance. When the appropriate amount of liquid has been delivered,delivery of liquid is stopped or altered to prevent undue pressure inthe volume and resulting stress on the plate or liquid leakage throughthe mesh plate. The supply of liquid is resumed when the liquid on themesh plate has been consumed or reduced, as detected by the sensor. Inan embodiment of the invention, the mesh plate may serve as one of theelectrodes. Or, an optical sensor may be used as a liquid detector.

The nebulizer apparatus may include a control valve connected in aliquid transport line for the liquid to be nebulized. This valve may beopened and closed, responsive to the sensor, to control the liquid flowthrough the transport line to the mesh plate.

A reservoir for the nebulizer apparatus connected to the liquidtransport line stores the liquid prior to nebulization. The reservoirmay be pressurized to supply liquid to the liquid transport line.Alternatively, a pump or elevated reservoir may be used to supply theliquid.

If small amounts of liquid are to be delivered, a pre-determined amountof the liquid may be stored in a two-part reservoir prior tonebulization. One part of the reservoir comprises a chamber forreceiving the liquid to be nebulized. This chamber is separated from theother part of the reservoir by a flexible wall. The other part of thereservoir is pressurized with liquid or gas to supply the liquid fromthe chamber to the liquid supply line.

To avoid condensation on the front surface of the mesh plate in themoist breathing circuit environment, to reduce liquid viscosity, and/orto provide comfort to the patient, a heater, such as a resistor, may beincorporated in the nebulizer apparatus or liquid transport line.

Various other features, objects, and advantages of the invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The foregoing objects and advantages, as well as the invention itself,will be more fully understood from the attached drawing and followingdetailed description.

In the drawings:

FIG. 1 is a general cross sectional view of the nebulizer apparatus ofthe present invention, the operating environment for the nebulizerapparatus being shown in a generalized schematic form;

FIG. 2 is a cross-sectional side elevational view of the nebulizerapparatus shown generally in FIG. 1;

FIG. 3 shows an cross-sectional side elevation of an alternativeembodiment of the nebulizer apparatus;

FIGS. 4 and 5 show alternative embodiments for the control apparatus andliquid supply for the nebulizer apparatus shown in FIG. 1;

FIGS. 6(a) through 6(d) show schematic views of alternative embodimentsof the nebulizer apparatus liquid reservoir;

FIG. 7 shows use of an optical liquid sensor;

FIG. 8a is an exploded, partial view showing a further embodiment of thenebulizer apparatus according to the present invention; and

FIGS. 8b and 8 c are schematic views showing the operation of thenebulizer apparatus of FIG. 8a.

DETAILED DESCRIPTION OF THE INVENTION

Nebulizer apparatus 1 of the present invention is typically used inconjunction with breathing circuit 2, ventilator 4 and control unit 6,as shown in FIG. 1. The nebulizer atomizes liquid solutions orsuspensions for delivery to a subject, as for example as a drugtreatment for a patient. Breathing circuit 2 includes inhalation limb 8,which is coupled to ventilator 4 at inhalation limb connector 10.Exhalation limb 12 is connected to ventilator 4 at exhalation limbconnector 14. Inhalation limb 8 and exhalation limb 12 are connected totwo arms of Y-connector 16. A third arm of Y-connector 16 is connectedto one end of patient limb 18. The other end of patient limb 18 isdirected to a mouthpiece, facemask, or endotracheal tube for thesubject.

Ventilator 4 provides all or a portion of the respiratory gases for thesubject by providing inhalation gases in inhalation limb 8. Theinhalation gases pass through Y-connector 16 and into patient limb 18for supply to the subject. On exhalation, the respiratory gases passthrough patient limb 18, Y-connector 16, and exhalation limb 12 back toventilator 4.

As shown in FIG. 1, nebulizer apparatus 1 is preferably positioned inpatient breathing circuit 2 as near the patient as possible to minimizethe aerosol transport path, and to minimize the deposition of theaerosol on the breathing circuit walls. To this end, nebulizer apparatus1 may be inserted in the breathing circuit between Y-connector 16 andpatient limb 18. Y-connector 16 has socket 20 for receiving tubularprojection 22 of adapter 24 for nebulizer apparatus 1. Tubular socket 26of adapter 24 receives patient limb 18. The nebulizer apparatus isplaced in opening 28 in adapter 24 and held in place with O-ring seal30. When nebulizer apparatus 1 is not needed, or when the nebulizerapparatus is removed for cleaning or maintenance, a cap (not shown) maybe fitted into or over the opening 28 to allow breathing circuit 2 tofunction in a normal manner. Alternatively, the entire adapter 24containing nebulizer apparatus 1 may be removed from the breathingcircuit and patient limb 18 reconnected to Y-connector 16. Control unit6 may be located at a distance from nebulizer apparatus 1 and may beincorporated in ventilator 4, if desired.

Nebulizer apparatus 1 is connected to a source of material to benebulized. In the embodiment shown in FIG. 1, conduit 32 and transportline 32 a supply material from reservoir 34 to apparatus 1. Reservoir 34can be placed at a desired location and can be proximate to, or remotefrom, nebulizer apparatus 1. Control valve 40 is provided in supplyconduit 32 and transport line 32 a. Electrical control signals aresupplied to control valve 40 via cable 42 from control unit 6. As notedabove, the material can comprise an aqueous solution, or a particulateor colloidal suspension, of a pharmaceutical agent. For purposes ofexplanation, the material undergoing nebulization is hereinaftergenerally described as a liquid. Reservoir 34 is pressurized by pump 36in control unit 6. In the embodiment shown in FIG. 1, pump 36 supplies apressurizing gas to reservoir 34 through pressure line 38.

Nebulizer apparatus 1 is shown, in detail, in FIG. 2. The apparatuscomprises housing 50 which mounts apparatus 1 in opening 28 of adapter24 via O-ring seal 30. Housing 50 may be formed of plastic. Housing 50has a cavity 52. Panel 54 spans cavity 52. Panel 54 is hinged at oneedge by hinge 56, and contains a clip 58 at an opposite edge engagingcut-out 60 in housing 50. Panel 54 may be opened by disengaging clip 58from cut-out 60, to allow the portions of apparatus 1 carrying out thenebulizing of the liquid and positioned in cavity 52 to be removed atthe end of therapy for replacement, or for cleaning when a differentdrug is to administered to the subject. Panel 54 has an opening 61 inthe central portion thereof.

Mesh plate frame 62 is received in cavity 52. Frame 62 may be formed of,for example, aluminum or brass. Mesh plate frame 62 has a centrallylocated aperture defined by surface 64. Mesh plate 66 spans the aperturewith peripheral edge 68 embedded into frame 62 at surface 64. Frame 62has an ultrasonic vibration generator in the form of piezoelectricelement 70 embedded therein to vibrate frame 62, as well as mesh plate66. Mesh plate frame 62, when placed in cavity 52, contacts terminal 72in housing 50 and terminal 74 in panel 54. Terminal 72 and 74 are thusconnected to piezoelectric element 70. They are also connected, viacable 42 to an electrical power source 75 in control unit 6 having adesired frequency in the ultrasonic range. Typically frequencies rangefrom 50 to 200 kHz. The connections may be carried out by conductors 71and 73 in frame 62.

Housing 50, frame 62, and mesh plate 66 and cavity 52 may be generallycircular in form. When fitted into housing cavity, the rear surface 76of mesh plate 66, mesh plate frame surface 64 and housing surface 78define an internal volume 80. Transport line 32 a extends throughhousing 50 to open into volume 80 at surface 78.

Mesh plate 66 is a relatively thin plate having a plurality of holes 82.Mesh plate 12 may be about 0.02 mm thick. The diameter of the holes atfront surface 84 is preferably approximately 2-15 μm in diameter. Suchholes may be formed in the plate by an electroforming process, whichprocess produces holes of increasing diameter toward rear surface 76shown in FIGS. 2 and 3 of the drawing. However, the straight holes,shown in FIGS. 7 and 8 will work equally well, the primary criterionbeing that the exit diameter in front surface 84 be such as to formdroplets of the desired size.

The thinness of mesh plate 66 limits its ability to resist excessiveforces generated by liquid pressures in volume 80. Liquid pressure involume 80 may also cause leaks through holes 82. To insure the propersupply of liquid from transport line 32 a, sensing elements, such as apair of spaced electrodes 86, are fitted in housing 50 to sense thepresence or absence of the liquid in volume 80. As shown in FIG. 2,electrodes 86 may be mounted in surface 78 of housing 50 adjacent theoutlet of transport line 32 a.

Front surface 84 of mesh plate 66 is exposed to the pressure of thebreathing gases in breathing circuit 2. These pressures will vary duringinhalation and exhalation conditions in breathing circuit 2. Forexample, with artificial ventilation, breathing circuit pressures mayincrease up to 100 mbar during inspiration and thereafter decreaseduring expiration. Housing 50 is provided with pressure balancingchannel 88 shown in FIG. 2 that connects volume 80 with breathingcircuit 2 for equalizing the prevailing pressure at both sides of meshplate 66 to avoid pressure stressing mesh plate 66 and causing leaks tooccur through the mesh plate.

In operation, valve 40 is opened responsive to a signal from cable 42and liquid flows through conduit 32 and transport line 32 a due to thepressurizing gas in reservoir 34. The liquid flows out the end oftransport line 32 a into contact with the upper surface of mesh plate66. The cohesive forces in the liquid form the liquid into a column ofliquid extending between the end of transport line 32 a and mesh plate66, generally as shown in FIG. 2. Piezoelectric element 70 is energizedfrom a high frequency source 75 in control 6 through cable 42 andterminals 72 and 74 in housing 50 to vibrate mesh plate 66. Thepositioning and energization of piezoelectric element 70 may be such asto cause mesh plate 84 to move toward and away from the end of transportline 32 a and the liquid being discharged therefrom. The vibrationscause the liquid in volume 80 to pass through holes 82 in mesh plate 66.

At the front surface 84 of the vibrating mesh plate 66, the atomizedliquid will grow into drops at each hole 82 due to the liquid surfacetension. The drops will increase in size until the expelling forcesarising from the movement of mesh plate 66 and the mass of each drop,exceeds the holding force determined by the size of the holes 82 in meshplate 66, and the surface tension of the liquid. The drops expelled fromplate 66 pass through opening 61 in panel 54 into the patient limb 42,and to the subject during inhalation.

To control the transport of liquid from reservoir 34 into the ofnebulizing apparatus 1, electrodes 86, positioned in surface 78 ofhousing 50, detect the presence of liquid between the end of transportline 32 a and the rear surface 76 of mesh plate 66 by alteration of theimpedance between the electrodes. That is, with the continued supply ofliquid, the column will start to bulge and the impedance measuredbetween the electrodes will be significantly altered. A signal fromelectrodes 86 is inputted to impedance sensor 87 and control unit 6 viaconductors 85 and 89 and cable 42 and used to control valve 40 in liquidsupply conduit 32 to close the valve. When the impedance changes, due tothe liquid receding away from electrodes 86, the control valve 40 opensto again allow flow of liquid from the end of transport line 32 a. Thesupply of liquid in the nebulizer of the present invention may thus becharacterized as being of the “on demand” type. The delivery ofnebulized liquid can be controlled by continuously vibrating mesh plate66 and regulating the liquid transport control or by regulating theactivation of mesh plate vibration and intermittently supplying liquidwhen the amount of liquid in volume 80 is reduced.

Alternatively, the presence of liquid in volume 80 could be measured byan optical sensor, as shown in FIG. 7, that senses changes in lighttransmission or reflection caused by the liquid in volume 80. When thereis no liquid on mesh plate 66, light from light source 86 a is reflectedoff the mesh plate to detector 86 b. The presence of liquid alters thelight path.

The proper supply of liquid through the on-demand delivery fromtransport line 32 a, as controlled by electrodes 86, provides thefollowing advantages. If too much liquid were to be delivered to volume80, liquid would pressurize mesh plate 66 and might leak through meshplate 66. And, if too much liquid were to be delivered to volume 80,pressure balancing channel 88 could be occluded. This could also resultin undesired pressures being applied to mesh plate 66.

If too little liquid is delivered to volume 80, the liquid fromtransport line 32 a may not cover all the holes 82 in mesh plate 66.However, the pressure balancing provided by channel 88 avoids breathinggas flow through the holes in mesh plate 66 in opposition to the liquidbeing nebulized which might otherwise degrade the operation of nebulizerapparatus 1.

Position insensitivity for nebulizer apparatus 1 is obtained by locatingthe end of transport line 32 a sufficiently close to rear surface 76 ofmesh plate 66 that the surface tension in the column of liquid willmaintain the column between the end of transport line 32 a and rearsurface 76 of mesh plate 66. Since liquid is incompressible, shouldnebulizer apparatus be inverted from the position shown in FIG. 2, theliquid in transport line 32 a will support the liquid column in volume80 so that operation of the nebulizer apparatus is maintained.

In some applications, it may be desirable to heat the liquid to benebulized, the mesh plate, the mesh plate frame, the housing and/orliquid supply conduit/transport line. For example, the liquid may beheated to body temperature to improve administration of the agent or toprevent discomfort to the patient. Mesh plate 66 or mesh plate frame 62or housing 50 could be heated for these purposes and to preventcondensation of the liquid or spray on these or other elements. Forthese purposes, an appropriate heater, for example, a resistor 91, maybe employed and controlled through cable 42.

An alternative embodiment of the nebulizer apparatus is shown in FIG. 3.In the nebulizer apparatus 1 a of FIG. 3, mesh plate 66 a is formedusing a conductive material such as nickel, which enables it to functionas an electrode for liquid level measurement in volume 80 a. Mesh plate66 a rests on annular disc 90 having an opening 92. Annular disc 90 ismade of a conductive material that is inert with respect to the liquidto be nebulized and to the breathing gases. Disc 90 forms the base ofhousing 50 a. Housing 50 a is completed with a non-conductive tubularsidewall 94 and a non-conductive top plate 96. Top plate 96 may beremovable to allow cleaning of the interior components of nebulizerapparatus 1 a. Mesh plate 66 a is electrically connected to disc 90 andto conductor 97.

Sidewall 94 has an aperture that accommodates transport line 32 b.Unlike the embodiment of FIG. 1, the cavity or volume 80 a in FIG. 3 isfilled with liquid from the side of apparatus 1 a, rather than from thetop.

Conductive plate 98 is mounted in sidewall 94 as by the upright flangearound its perimeter which is directed away from the mesh plate 66 a.Plate 98 has several purposes. First, plate 98 mounts ultrasonicvibration generator 100, preferably a piezoelectric element. Ultrasonicvibration generator 100 is affixed to plate 98. Second, plate 98functions as a liquid level detector in space 80 a by serving as anelectrode for measurement in conjunction with conductive mesh plate 66a.

In operation, liquid flows into volume 80 a from transport line 32 b. Acontrol valve, such as valve 40, shown in FIG. 1 is used to control theliquid transported into volume 80 a. When the liquid makes contact withmesh plate 66 a and with plate 98 serving as sensing electrodes, theimpedance measurement between plate 98 and mesh plate 66 a changes. Thecontrol valve is closed, to be thereafter opened when the liquid levelrecedes to the point where contact with plate 98 is lost.

Piezoelectric element 100 vibrates the liquid by inducing pressure wavesfrom plate 98. The piezoelectric element is energized by electricalpower source 75 in control unit 6 through cable 42. The vibrating liquidis atomized as it passes through holes 82 and discharged into thebreathing gases.

Thus, while in nebulizer apparatus of FIG. 1, mesh plate 66 is vibratedby the piezoelectric element, in nebulizer apparatus 1 a shown in FIG.3, the liquid in volume 80 a is vibrated by the piezoelectric element.

The embodiment of the invention shown in FIG. 4 differs from that shownin FIG. 1 in that pump 36 a in control unit 6 supplies liquid directlyto transport line 32 c from a liquid source (not shown). The controlprovided by valve 40, shown in FIG. 1, can be achieved by turning pump36 on and off. Cable 42 obtains electrical signals from the liquid levelsensors in nebulizer apparatus 1 for use by control unit 6 incontrolling pump 36 a. The pump is turned off when the impedancedetected by the liquid level sensors indicates that the appropriateamount of liquid has been provided to nebulizer apparatus 1. Use of thepump 36 a shown in FIG. 4 has advantages over the pressurizing gas shownin FIG. 1 in that some liquid medications cannot be exposed to thepressurizing gas without deleterious effects.

In the embodiment of FIG. 5, the force used to transport the liquid tothe nebulizer apparatus is obtained hydrostatically. The liquid source,such as liquid reservoir 34 a, can be arranged at an elevated positionwith respect to nebulizer apparatus 1, 1 a to generate a pressure headto supply liquid to the apparatus. Liquid supply 34 a may comprise aflexible pouch or bag mounted on stand 102 to create a hydrostaticpressure for causing liquid to flow through transport line 32 d whencontrol valve 40 is opened. The arrangement shown in FIG. 5 isespecially suitable for nebulizing the large amounts of liquid oftenrequired in continuous long term treatment of a subject. The embodimentof FIG. 5 has the advantage in that it will use less energy, and be lessnoisy, than embodiments using gas or liquid pumps.

FIGS. 6a-d show, in schematic form, various other techniques by whichamounts of liquid to be nebulized may be provided to transport line 32.In the alternatives schematically depicted in FIG. 6, the reservoir forthe liquid to be nebulized has a flexible wall 110 which keeps theliquid in reservoir chamber 112 separate from a pressurizing agent inchamber 114 which is used to supply the liquid through transport line32. This avoids contamination of the liquid to be nebulized by thepressurizing agent, and/or insures sterility of the liquid to benebulized.

In the embodiment of the invention shown in FIG. 6(a), syringe 116 isused to pressurize pressure chamber 114 of reservoir 34 b through line117 and automatically opening and closing valve 118. Syringe supplies apressurizing agent, such as a gas, to chamber 114 to pressurize theliquid to be nebulized contained in reservoir chamber 112 of reservoir34 b. Syringe 116 may be removed once the pressurization is completed.Liquid reservoir 112 may be loaded with the required dosage of apharmaceutical agent through conduit 119, sealed with valve 120 orthrough transport line 32, and pressure chamber 114 pressurized prior toconnection of reservoir 34 b to apparatus 1. Valve 120, which opens whenreservoir 34 a is connected to nebulizing apparatus 1, is provided inconduit 32. FIG. 6b shows a reservoir 34 c which has been filled throughtransport line 32. The reservoir is shown in a condition in which mostof the liquid to be nebulized has been discharged from reservoir chamber112.

In the embodiment of the invention shown in FIG. 6(c), pressure chamber114 is pressurized by gravitationally supplying a liquid to chamber 114.The liquid is stored in a container 122, elevated above reservoir 34 dto obtain an adequate head pressure. Container 122 may be kept at theappropriate level using an adjustable stand 102.

In the embodiment of the invention shown in FIG. 6(d) the pressurechamber 114 is pressurized by pump 15 a. The pump may be located, forexample, in control unit 6 (shown in FIGS. 1 and 2) and connected toreservoir 34 c by supply line 124. Pump 15 a may be either a liquid orgas pump. In operation, pump 15 a is regulated by control unit 6.

It will be appreciated that the reservoir for the liquid to be nebulizedcan comprise a pre-filled reservoir containing a desired dosage of apharmaceutical or other agent to be dispensed by nebulizer apparatus 1in reservoir chamber 112.

FIGS. 8a, 8 b, and 8 c show a further embodiment of the nebulizerapparatus of the present invention and in which elements similar oranalogous to the embodiments of FIGS. 1 and 3 are indicated with similarreference numerals. Nebulizer apparatus 150 shown in the crosssectional, exploded view of FIG. 8a has annular housing 50 b whichmounts the apparatus in adapter 24. Housing 50 b is formed of plastic orsimilar material. Lip 152 is formed on the lower edge of housing 50 band contains O-ring 154.

Disc-like plate 156, shown with enlarged thickness in FIG. 8a andcomprised of a conductive material such as brass, is sealed to lip 152by O-ring 154. Plate 156 contains a central opening 158. The surface ofplate 156 which is the lower surface when the nebulizer apparatus isoriented as shown in FIG. 8a mounts mesh plate 66 b containing holes 82.Mesh plate 66 b may be mounted to plate 156 by gluing, brazing, welding,or other suitable technique.

Piezoelectric element 70 b is mounted on the upper surface of plate 156.Specifically, piezoelectric element 70 b is spaced from plate 156 by asmall gap 160 and secured to plate 156 about its periphery by aconductive glue, brazing, welding, or other suitable technique, shown as162 in FIG. 8. Piezoelectric element 70 b has a central openingcorresponding to that of plate 156.

Plug member 164 formed of a non-conductive material, such as plastic, isplaced in cavity 52 b of housing 50 b. Plug member 164 has depending lip166 containing O-ring 168. Plug member 164 is placed on top of plate 156so that the plate is between O-rings 154 and 168.

A central liquid transport line 32 c extends through plug member 164 toapproximately the upper surface of plate 156. A small domed cavity 170may be formed in the lower surface of plug member 164 to surroundtransport line 32 c. Transport line 32 c may be formed of a conductivematerial to allow its use in impedance measurement of the presence ofliquid in nebulizer apparatus 150.

An electric power terminal 74 b extends through plug member 164. Thelower end of terminal 74 b, which terminal may be in the form of aspring loaded pin, contacts piezoelectric element 70 b. The upper end ofterminal 74 b is connected to cable 42. A second electrical powerterminal 72 b also extends through plug member 164. The lower end ofterminal 72 b contacts conductive plate 156. The upper end of terminal72 b is connected to cable 42. Terminal 72 b may be electricallygrounded for purposes of applying a voltage to piezoelectric element 70b in conjunction with terminal 74 b, as well as for impedancemeasurement in conjunction with conductive liquid transport line 32 c.

In operation, alternating voltage is supplied from power source 75through cable 42 and terminals 72 b and 74 b to piezoelectric element 70b which vibrates the element. The vibrations cause the element tocontract from the normal condition, shown in FIG. 8b to a radiallydecreased condition shown in FIG. 8c and return to the normal condition.Due to the joinder of piezoelectric element 70 b to plate 156 about theperiphery of the element, the radial size reduction of piezoelectricelement 70 b causes plate 156 to bow, as shown in FIG. 8c, and thenreturn to the flat condition, shown in FIG. 8b, when piezoelectricelement 70 b returns to the normal state. The action of plate 156 shownin FIGS. 8b and 8 c discharges nebulized liquid from holes 82 in meshplate 66 b.

It is recognized that other equivalents, alternatives, and modificationsaside from those expressly stated, are possible and within the scope ofthe appended claims.

What is claimed is:
 1. A nebulizer apparatus for atomizing a liquid intoan aerosol of fine droplets, said nebulizer apparatus comprising: ahousing having a cavity with an opening; a thin mesh plate positionedacross the opening of the cavity, said mesh plate having an exposedfront surface and a rear surface facing into said cavity, said meshplate having holes extending through said mesh plate from the frontsurface to the rear surface; a liquid transport line opening into saidcavity for supplying a volume of liquid to the rear surface of said meshplate; a vibration generator energizable to establish vibrations in oneof the mesh plate or liquid to cause the liquid to pass through theholes in the mesh plate and to be discharged from the front surface ofthe plate as an aerosol of fine droplets; a sensor located in saidcavity, said sensor measuring the extent of a physical dimension of thevolume of liquid supplied to the rear surface of said mesh plate; andmeans for controlling a supply of liquid from said liquid transport lineto said cavity, responsive to said sensor, to maintain a desired volumeof liquid on the rear surface of said mesh plate.
 2. The apparatus ofclaim 1 wherein the holes have diameters and wherein the diameters ofthe holes are larger at the rear surface of the mesh plate and decreasealong extensions of the holes through the mesh plate to smallerdiameters at the front surface of the plate.
 3. The apparatus of claim 1wherein said holes are straight holes.
 4. The apparatus of claim 1wherein the vibration generator comprises a piezoelectric element. 5.The apparatus of claim 4 wherein said vibrator means is coupled to saidmesh plate to vibrate the plate.
 6. The apparatus of claim 5 whereinsaid holes are in a central portion of said mesh plate and wherein saidvibration generator is peripherally joined to said mesh plate tosurround said central portion, energization of said vibration generatorcausing a bowing action in said mesh plate.
 7. The apparatus of claim 4wherein said vibration generator contacts the liquid to induce pressurewaves in the liquid.
 8. The apparatus of claim 1 wherein the liquidtransport line is further defined as supplying liquid to form a columnof liquid on the rear surface of said mesh plate.
 9. The apparatus ofclaim 1 wherein said sensor comprises spaced elements establishing animpedance therebetween and wherein said sensor measures the extent of aphysical dimension of the volume of liquid supplied to the rear surfaceof said mesh plate by changes in impedance between said spaced elementsproduced by the liquid.
 10. The apparatus of claim 9 wherein said spacedelements comprise a pair of spaced electrodes in said cavity.
 11. Theapparatus of claim 10 wherein said liquid transport line has an openingin said cavity on a surface opposite said rear surface of said meshplate and wherein said electrodes are adjacent the opening of saidliquid transport line.
 12. The apparatus of claim 9 wherein said meshplate forms one of said spaced elements.
 13. The apparatus of claim 12wherein a portion of said liquid transport line adjacent the opening ofsaid liquid transport line forms the other of said spaced elements. 14.The apparatus of claim 9 wherein a portion of said liquid transport lineadjacent the opening of said liquid transport line forms one of saidspaced elements.
 15. The apparatus of claim 1 wherein said sensorcomprises an optical sensor.
 16. The apparatus of claim 1 includingmeans for equalizing pressure at the rear surface of the mesh plate andpressure at the front surface of the mesh plate.
 17. The apparatus ofclaim 16 further including a pressure balance channel in said housingbetween said front and rear surfaces of said mesh plate, whereby thepressures at the front surface and the rear surface are equalized. 18.The apparatus of claim 1 wherein the means for controlling a supply ofliquid comprises a valve in said liquid transport line.
 19. Theapparatus of claim 18 further including means for pressurizing theliquid in said liquid transport line.
 20. The apparatus of claim 19wherein the liquid is contained in a reservoir connected to the liquidtransport line and wherein said means for pressurizing is a gas pump forpressurizing the reservoir.
 21. The apparatus of claim 19 wherein theliquid is contained in a reservoir elevated with respect to saidnebulizer apparatus for pressurizing the liquid with a hydrostatic head.22. The apparatus of claim 1 wherein the means for controlling a supplyof liquid comprises a pump coupled to said liquid transport line. 23.The apparatus of claim 1 further including a reservoir for storage ofthe liquid prior to atomization, wherein the reservoir is connected tosaid liquid transport line for delivery of the liquid to the rearsurface of the mesh plate.
 24. The apparatus of claim 23 wherein saidreservoir comprises a two-part container having a deformable liquidreservoir within a part of the container which can be pressurized forpressurizing said liquid reservoir.
 25. The apparatus of claim 24further including a gas pump for pressurizing the part of the container.26. The apparatus of claim 24 further including an elevated liquidreservoir connected to said part of said container to provide ahydrostatic force for pressurizing said liquid reservoir.
 27. Theapparatus of claim 1 further defined as a nebulizer apparatus fordelivering an aerosol to the breathing gas of a subject passing in abreathing circuit, said apparatus including an adapter for coupling saidhousing to the breathing circuit.
 28. The apparatus of claim 27including a reservoir connected to said liquid transport line forstoring the liquid to be atomized.
 29. The apparatus of claim 1 furtherincluding a heater.